[PATCH] libstdc++: Fix std module to work with --disable-wchar_t [PR126111]
Jonathan Wakely
jwakely.gcc@gmail.com
Tue Jul 14 07:21:17 GMT 2026
On Tue, 14 Jul 2026, 08:15 Tomasz Kaminski, <tkaminsk@redhat.com> wrote:
>
>
> On Mon, Jul 13, 2026 at 7:15 PM Jonathan Wakely <jwakely@redhat.com>
> wrote:
>
>> We should not try to export names which are not declared if GCC is
>> configured with --disable-wchar_t.
>>
>> We should also not define the wide stream aliases in <syncstream> and
>> <spanstream>.
>>
>> libstdc++-v3/ChangeLog:
>>
>> PR libstdc++/126111
>> * include/std/format (__format::__write_escape_seq): Move alias
>> declaration into #ifdef _GLIBCXX_USE_WCHAR_T group.
>> * include/std/spanstream (wspanbuf, wispanstream, wospanstream)
>> (wspanstream): Only declare for _GLIBCXX_USE_WCHAR_T.
>> * include/std/syncstream (wsyncbuf wosyncstream): Likewise.
>> * src/c++23/std.cc.in: Add preprocessor checks for
>> _GLIBCXX_USE_WCHAR_T to names which depend on it.
>> ---
>>
>> Tested x86_64-linux.
>>
> Outside of single question below, this LGTM.
>
>>
>> libstdc++-v3/include/std/format | 2 +-
>> libstdc++-v3/include/std/spanstream | 8 ++++++
>> libstdc++-v3/include/std/syncstream | 5 ++--
>> libstdc++-v3/src/c++23/std.cc.in | 44 ++++++++++++++++++++++++-----
>> 4 files changed, 49 insertions(+), 10 deletions(-)
>>
>> diff --git a/libstdc++-v3/include/std/format
>> b/libstdc++-v3/include/std/format
>> index 1b4082e07a44..2530ecb58057 100644
>> --- a/libstdc++-v3/include/std/format
>> +++ b/libstdc++-v3/include/std/format
>> @@ -1052,7 +1052,6 @@ namespace __format
>> __write_escape_seq(_Out __out, uint_least32_t __val,
>> basic_string_view<_CharT> __prefix)
>> {
>> - using _Str_view = basic_string_view<_CharT>;
>>
> Why do we need this change? The function should not be instantiated
> with _CharT = wchar_t, so this should be OK.
>
Because it gives a -Wunused-local-typedef warning when the WCHAR_T macro is
undefined.
constexpr size_t __max = 8;
>> char __buf[__max];
>> const string_view __narrow(
>> @@ -1067,6 +1066,7 @@ namespace __format
>> #ifdef _GLIBCXX_USE_WCHAR_T
>> else
>> {
>> + using _Str_view = basic_string_view<_CharT>;
>>
> If we go with this direction, simply replace _CharT with wchar_t
> in line below, and _Str_view with wstring_view in __format_write.
>
>> _CharT __wbuf[__max];
>> const size_t __n = __narrow.size();
>> std::__to_wstring_numeric(__narrow.data(), __n, __wbuf);
>> diff --git a/libstdc++-v3/include/std/spanstream
>> b/libstdc++-v3/include/std/spanstream
>> index fd2a446ddaa3..6f1f681ae793 100644
>> --- a/libstdc++-v3/include/std/spanstream
>> +++ b/libstdc++-v3/include/std/spanstream
>> @@ -225,7 +225,9 @@ template<typename _CharT, typename _Traits>
>> { __x.swap(__y); }
>>
>> using spanbuf = basic_spanbuf<char>;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using wspanbuf = basic_spanbuf<wchar_t>;
>> +#endif
>>
>> template<typename _CharT, typename _Traits>
>> class basic_ispanstream
>> @@ -319,7 +321,9 @@ template<typename _CharT, typename _Traits>
>> { __x.swap(__y); }
>>
>> using ispanstream = basic_ispanstream<char>;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using wispanstream = basic_ispanstream<wchar_t>;
>> +#endif
>>
>> template<typename _CharT, typename _Traits>
>> class basic_ospanstream
>> @@ -389,7 +393,9 @@ template<typename _CharT, typename _Traits>
>> { __x.swap(__y); }
>>
>> using ospanstream = basic_ospanstream<char>;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using wospanstream = basic_ospanstream<wchar_t>;
>> +#endif
>>
>> template<typename _CharT, typename _Traits>
>> class basic_spanstream
>> @@ -459,7 +465,9 @@ template<typename _CharT, typename _Traits>
>> { __x.swap(__y); }
>>
>> using spanstream = basic_spanstream<char>;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using wspanstream = basic_spanstream<wchar_t>;
>> +#endif
>>
>> _GLIBCXX_END_NAMESPACE_VERSION
>> } // namespace std
>> diff --git a/libstdc++-v3/include/std/syncstream
>> b/libstdc++-v3/include/std/syncstream
>> index 9cecd513e9a5..7a1f956dca55 100644
>> --- a/libstdc++-v3/include/std/syncstream
>> +++ b/libstdc++-v3/include/std/syncstream
>> @@ -299,10 +299,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> { __x.swap(__y); }
>>
>> using syncbuf = basic_syncbuf<char>;
>> - using wsyncbuf = basic_syncbuf<wchar_t>;
>> -
>> using osyncstream = basic_osyncstream<char>;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> + using wsyncbuf = basic_syncbuf<wchar_t>;
>> using wosyncstream = basic_osyncstream<wchar_t>;
>> +#endif
>> _GLIBCXX_END_NAMESPACE_VERSION
>> } // namespace std
>> #endif // __cpp_lib_syncbuf
>> diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/
>> std.cc.in
>> index dbed0112dca5..5aab08f2c498 100644
>> --- a/libstdc++-v3/src/c++23/std.cc.in
>> +++ b/libstdc++-v3/src/c++23/std.cc.in
>> @@ -1368,17 +1368,19 @@ export namespace std
>> #endif
>> using std::formatter;
>> using std::make_format_args;
>> - using std::make_wformat_args;
>> #if __cpp_lib_format >= 202603L // >= C++26
>> using std::dynamic_format;
>> #endif
>> using std::vformat;
>> using std::vformat_to;
>> using std::visit_format_arg;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> + using std::make_wformat_args;
>> using std::wformat_args;
>> using std::wformat_context;
>> using std::wformat_parse_context;
>> using std::wformat_string;
>> +#endif
>> #ifdef __cpp_lib_format_ranges
>> using std::format_kind;
>> using std::range_format;
>> @@ -1416,10 +1418,12 @@ export namespace std
>> using std::ifstream;
>> using std::ofstream;
>> using std::swap;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wfilebuf;
>> using std::wfstream;
>> using std::wifstream;
>> using std::wofstream;
>> +#endif
>> }
>>
>> // <functional>
>> @@ -1620,7 +1624,9 @@ export namespace std
>> using std::streamsize;
>> using std::unitbuf;
>> using std::uppercase;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wios;
>> +#endif
>> }
>>
>> // <iosfwd>
>> @@ -1639,9 +1645,11 @@ export namespace std
>> using std::basic_syncbuf;
>> using std::osyncstream;
>> using std::syncbuf;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wosyncstream;
>> using std::wsyncbuf;
>> #endif
>> +#endif
>> }
>>
>> // <iostream>
>> @@ -1651,10 +1659,12 @@ export namespace std
>> using std::cin;
>> using std::clog;
>> using std::cout;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wcerr;
>> using std::wcin;
>> using std::wclog;
>> using std::wcout;
>> +#endif
>> }
>>
>> // <istream>
>> @@ -1664,8 +1674,10 @@ export namespace std
>> using std::basic_istream;
>> using std::iostream;
>> using std::istream;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wiostream;
>> using std::wistream;
>> +#endif
>> using std::ws;
>> using std::operator>>;
>> }
>> @@ -2487,7 +2499,9 @@ export namespace std
>> using std::ends;
>> using std::flush;
>> using std::ostream;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wostream;
>> +#endif
>> using std::operator<<;
>> #ifdef __cpp_lib_syncbuf
>> using std::emit_on_flush;
>> @@ -2916,9 +2930,11 @@ export namespace std
>> using std::ssub_match;
>> using std::sub_match;
>> using std::swap;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wcsub_match;
>> using std::wregex;
>> using std::wssub_match;
>> +#endif
>> using std::operator==;
>> using std::operator<=>;
>> using std::operator<<;
>> @@ -2934,20 +2950,24 @@ export namespace std
>> using std::smatch;
>> using std::sregex_iterator;
>> using std::sregex_token_iterator;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wcmatch;
>> using std::wcregex_iterator;
>> using std::wcregex_token_iterator;
>> using std::wsmatch;
>> using std::wsregex_iterator;
>> using std::wsregex_token_iterator;
>> +#endif
>> namespace pmr
>> {
>> #if _GLIBCXX_USE_CXX11_ABI
>> using std::pmr::cmatch;
>> using std::pmr::match_results;
>> using std::pmr::smatch;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::pmr::wcmatch;
>> using std::pmr::wsmatch;
>> +#endif
>> #endif
>> }
>> }
>> @@ -3020,17 +3040,19 @@ export namespace std
>> export namespace std
>> {
>> using std::basic_spanbuf;
>> - using std::spanbuf;
>> - using std::wspanbuf;
>> using std::basic_ispanstream;
>> - using std::ispanstream;
>> - using std::wispanstream;
>> using std::basic_ospanstream;
>> - using std::ospanstream;
>> - using std::wospanstream;
>> using std::basic_spanstream;
>> + using std::spanbuf;
>> + using std::ispanstream;
>> + using std::ospanstream;
>> using std::spanstream;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> + using std::wspanbuf;
>> + using std::wispanstream;
>> + using std::wospanstream;
>> using std::wspanstream;
>> +#endif
>> }
>> #endif
>>
>> @@ -3046,10 +3068,12 @@ export namespace std
>> using std::stringbuf;
>> using std::stringstream;
>> using std::swap;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wistringstream;
>> using std::wostringstream;
>> using std::wstringbuf;
>> using std::wstringstream;
>> +#endif
>> }
>>
>> // <stack>
>> @@ -3144,7 +3168,9 @@ export namespace std
>> {
>> using std::basic_streambuf;
>> using std::streambuf;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wstreambuf;
>> +#endif
>> }
>>
>> // <string>
>> @@ -3171,7 +3197,9 @@ export namespace std
>> using std::stoull;
>> using std::string;
>> using std::to_string;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::to_wstring;
>> +#endif
>> using std::u16string;
>> using std::u32string;
>> using std::u8string;
>> @@ -3236,9 +3264,11 @@ export namespace std
>> using std::basic_osyncstream;
>> using std::osyncstream;
>> using std::syncbuf;
>> +#ifdef _GLIBCXX_USE_WCHAR_T
>> using std::wosyncstream;
>> using std::wsyncbuf;
>> #endif
>> +#endif
>> }
>>
>> // 19.5 <system_error>
>> --
>> 2.55.0
>>
>>
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